Studies of the nucleation of water droplets by respirable coal dust will be continued. Emphasis will be placed on advancing the methodology of the measurements, evaluating the effects of competition for the available water vapor, and studying differences in nucleation efficiencies among various kinds of coal. Improved techniques will be developed for generating monodisperse coal dust samples, for measuring supersaturation, and for detection and sizing sub-micron coal dust. Studies of nucleation and droplet growth will be conducted in a thermal diffusion cloud chamber using techniques developed in the laboratory. Long-range objectives of the research are to provide data which can lead to improvements of dust control methods in coal mines and can also aid in understanding the behavior and deposition of coal dust in the lungs.